Almost from day 1 our DD has been advanced at least 2 grades above her school grade in Maths. I didn't even bother attempting to get the school to differentiate because honestly they cannot.
They are typically under so much pressure to make silk purses out of sow's ears so to speak with the standardized testing that they haven't got the time to do a stellar job at that and look after the 1 child in the class that needs so much more but to the right of the line instead of the left.
We used Singapore Maths, the SG Maths Challenge Problems, Zaccaro (too easy really) and an online game called Lure of the Labyrinth for K thru 5 Maths levels. After that we went to AoPS.
I understand that AoPS now has something called Beast Academy for Primary Maths which gets good reviews. Were I in your shoes I would stop trying to stop the tide like the King Canute fable and just accept that you can lead a horse to water but you cannot make it drink.
Choose your battles and save your psychic reserves for the times when you have no alternatives - with Maths, at least, there are plenty of options outside of school - is what I would recommend. I mean, honestly, at primary levels - what exactly Is meeting the GT specialist really going to achieve that SG Maths or Beast Academy and later AoPS cannot?
